Expansible grounding electrode



Feb. 23, 1954 J. D. COVINGTON 2,670,397

EXPANSIBLE GROUNDING ELECTRODE Filed April 17 1950 A Sheets-Sheet l EM kn/58D CowNeroN INVENTOR.

BY A? $0M AGENT Feb. 23, 1954 J. D. COVINGTON 2,670,397

EXPANSIBLE GROUNDING ELECTRODE Filed April 17. 1950 2 Sheets-Sheet 2 JWES Do COM/N6 TON IN V EN TOR.

QQAJW AGENT Patented Feb. 23, 1954 EIGANSIBLE GROUNDING ELECTRODE James D. Covington, Dallas, Tex., assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a. corporation of New York Application April 17, 1950, Serial No. 156,389

Claims.

This invention relates to an electrode for readily establishing a high current circuit through a portion of the earth such as may be employed in electrical prospecting or electrical loggin systems.

For example, in electrical prospecting methods such as generically illustrated by Patent No. 2,454,911 to Dayton H. Clewell, relatively high amplitude current flow is produced in the earth between two grounded electrodes. Potentials resulting from the current flow are measured at spaced points to define earth structure. In such systems, a low impedance current path through the earth permits most efficient use of associated equipment in producing measurable potentials. For such low impedance circuits, it has been found that the electrodes used should have as large a surface area as possible since the major portion of the resistance in the circuit is often in the electrode-ground contact. At the same time, it is desirable to keep the size of the equipment to a minimum. A physically small grounding electrode with large surface area suggests a plural surface or honeycomb device. Ordinarily, through repeated use, such devices collect foreign matter in the cavities that is so diflicult to remove that the affected electrodes soon become unusable and must be discarded.

In accordance with the present invention, there is provided a folded or plural surface sheet metal electrode which has a large ratio of surface area to volume occupied thereby so constructed that it may readily be cleaned of mud and debris collecting therein.

In a preferred form of the invention, a rectangular metal plate is pleated normal to a length thereof. A terminal bar reinforcingly is secured along one end of the plate and extends beyond one edge adjacent said end with electrical connector means carried by the extension. Means are provided for rigidly but releasably interlocking the ends of the pleated plate to form a crimped expansible electrode.

For further objects and advantages of the invention and for a more complete description thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a diagrammatic view of an electrical prospecting system;

Fig. 2 is an exploded view of the electrode; and

Fig. 3 is an isometric view of the electrode of the present invention.

In the electrical prospecting system of Fig. 1, current from a source generically represented by the generator l0 connected to current electrodes II and I2, suitably grounded, flows through the earth producing an effect at a measuring station l3 which is detected by a circuit including potential electrodes l5 and I6 and an indicating device generically represented by meter II. The current from source [0 may be D. C., pulses, sine wave A. 0., or may be otherwise modified in accordance with teachings of the prior art. In any case, it is desirable to have as much as possible of the energy from source It! radiated for detectionby the potential electrodes while accompanied by but small power loss due to the flow of the current in producing the eifect desired to be measured. It is therefore necessary to provide low resistance current electrode-earth contacts in the exciting circuit thereby reducing the resistive losses and permitting high currents for radiation of signal energy.

Pits and holes filled with a highly conductive liquid, such as salt solution, have been utilized to lower the resistance between electrodes and the earth. Electrodes that may conveniently be placed in electrolyte filled auger holes have been provided which consist of a number of concentric copper tubes suitably connected together. However, deposits of heavy clays and other muds often characteristic of areas under survey are forced into the spaces between the electrode elements and are most diflicult to remove. Such deposits substantially increase the initial contact resistance between electrode and ground. Further, when mud cakes are present, the contact resistance drifts toward equilibrium as the cake absorbs moisture. Ordinarily such variations in the resistance of the input current. circuit cannot be tolerated.

By the present invention there is provided an electrode having large surface area of small volume for use in small diameter bore holes. The electrode is physically expansible for mechanically working the mud and debris loose from the many folds that make possible the large area. The foregoing features will be more apparent by referring to Figs. 2 and 3.

A rectangular plate 20, Fig. 2, of low resistivity material is crimped or pleated uniformly along a length thereof with the pleats normal to the length. The plate is crimped to relatively small angles, the internal angles, a, being preferably in the order of 30. A latching bar 2| is provided with a hook 22 at one end. The hook may conveniently be formed by bending the bar 21 back on itself as shown. A threaded lug .or bolt 23 is secured to the other end of latching bar 2| and extends normal to the plane of the bar on the same side thereof as the hook portion 22. The bar 2| is then welded onto the end 24 of the plate 20 with the interior of the hook portion s22..ev,en .-with the edge'of the-plate 20 and extending away-therefrom.

A terminal bar 26 similarly is reinforcingly welded along the end portion 21 of plate 20. In the form shown, terminalbarjt has a first extension 28 which includes or carries a handle and a second extension 23 which.carries. .electrical connecting means generically illustrated by the lug 30 (shown in Fig-'3) inse'rted-in' hole 29a for readily interconnecting the electrode and a conductor extending from source l -.ll gf,iEig. l.

With the construction above described, i. e., with the latching bar 2|,and terminal bar 26 (of the exploded view of Fig. 2) welded to the adjacent end portionsZ-l andZlrespectively; the plate 26 may be bent to forma star-shaped or crimped tube. The end of-plate2displaced-inthe hook portion 22 of the latching bar ZIa-nd the boltr23 passed through a hole 23min the terminal bar 26. A wing nut2'3b, shown in-Fig; 3 only threadedly engages bolt 23 to secure "the interlock between 'the ends of the plate 20. It will be noted that the extension 28 of the terminal bar Ziizis located approximately at the center of thestareshaped tube andextends radially therefrom through the root of one of the corrugations in the. tube. The handle 3| carried-by extensionid-is thereby .located approximately at-the axis of theelectrode to balance the electrode-whenlit iscarried. With the ends of the; electrode plate 28 thus-interlocked, the electrode with relatively large radiating surface area may-be placed in holes of relatively small diameter.

For a givenvolumeoc-cupiedby. the electrode, the number of points oricrimps in: the plate will determine the ratio of surface area-to. volume. This ratio numerically is l a measure? of z the effi- -ciency of a givenelectrode. :Byprovidingaclarge number of pleats-or ioldsgtheratio-becomes very large. 'At-the. same time, the ,difiicultyof cleaning a heavy clays ordinarily: becomes more --an d more difficult. However, in accordance .with -the present invention; theelectrode may be cleaned by removing the bolt" 23 from hole:23wand .dis-

engagin the hook-22 whereupon theelectrode maybe opened or expanded. By merely. shaking and mechanically working the expanded; electrodeall of. the inhibiting clays and-debris may .be readily removed. As the electrode isopened from the folded form as illustrated in-Eig3 tcia form substantially as illustrated in Fig.*2, the clays adhering to the internal angular. surfaces automatically are freedfrom-thev two -..adjacent surfaces.

bent to tubular form and interlocked for further use.

In one form of the inventiongthe;platezm,was of 16 gauge sheet copper approximately ill-inches wide. I The latchingdoar 23 and the terminalbar,

Thereafter, the plate may be again of "Said. terminal bar ;;asset forth in the appended claims.

What is claimed is:

1. An electrode comprising a rectangular metallic plate pleated normal to the length there-of, ater rnin,al ,strip,reinforcingly secured along one end of said Plate at an angle with respect to the meantplaneof saidpleated plate, means for releasablyinterlocking said strip and the other end qf saidplate with said terminal strip directed inwardlythereof to form an expansible electrode having a highratio of surface area to volume, and

means tor coupling an electrical circuit to said electrode.

2. A low resistance electrode comprising a rectangular plate pleated normal to the length thereof, a. latching bar reinforcingly. formin One end of said plate andextending beyondone. edge of said plate .adjacentsaid end, a hook on said extended end of said bar for interlocking said .bar and the other end of.said -plate, aiastcning device locking the ends of said plate .at-theedge opposite said hook for securing the interlock between said ends to form anexpansibleelectrode having a large ratio of vsurfaceareato .volume,

and means for connecting an ,electricalconductor to said electrode.

.An electrode which is readily. cleanedand which has a large ratio of surface area to volume comprising arectangular metallic platepleated normal to the length thereof, a terminal bar rein- .forcingly forming one end of. said plate and .ex-

tending beyond one edge adjacent said s end, electrical. connecting meansand carrying means connected to the extension of said bar,.a hook'at the edge of said .plate opposite said extensionior interlocking said bar and thexother end of said plateand releasable fasteningmeans at the edge of said plate opposite said .hookafor securing said 1 interlock toforma-rigid expansibleelectrode.

:4. An electrode having a largeratioofsurface area-to volume which isreadilyicleanable comprisinga corrugated star-shaped tube, a terminal bar extending longitudinally.through said tube from the axis thereof through-the rootof one -ofthe corrugations with longitudinal .sectionsiof said corrugated tube folded outwardly facing opposite sidesof said bar, means for bonding said bar to one of said foldedsections, a .hookat the end of said plate and atoneedgethereof-for interlocking said folded sections .at said edge, releasable fasteningmeans at theedge ofsaid I terminal bar extending longitudinally through said tube from the axis thrcughthe root o one of the .corrugationswith longit dirialsectio said tube foldedputwardly terminal bar to one of sa i dlong tu 33i91 r m a s: leasab e nis lq s i bar and the other of said longitudinal folded i... e ens re orm a i id qo r diub and c rying means and electric nr ecting rneans 5 carried. by said terminal bar beyond the plane of Number the end of said tube. 1,138,186 JAMES D. COVINGTON. 1,288,303 1,856,506 References Cited in the file of this patent 5 2,303,3 1

UNITED STATES PATENTS Number Name Date Number 873,375 Jones Dec. 10, 1907 223 314 883,303 Drake Mar. 31, 1908 Name Date Brach May 4, 1915 Vogel Dec. 17, 1918 Preston May 3, 1932 Pennell Dec. 1, 1942 FOREIGN PATENTS Country Date Switzerland Nev. 1, 1943 

